This invention relates generally to split collector transistors, and more particularly, to a method of matching currents appearing at the split collectors of lateral PNP transistors.
The use of split collector transistors is well known and is desirable for a number of reasons. For example, if it weren't for the use of multiple collectors, a great many more transistors would be required to provide the necessary current sources for a particular circuit application thus occupying more die area on an integrated circuit. Additionally, a classic method of generaing currents having specific ratios with respect to each other involve the use of split collector lateral PNP transistors. That is, the emitter of each transistor emits the available current and each collector sections associated with each emitter each collect a portion of the current depending upon the ratio of its area with respect to the other collectors. Thus, theoretically, it is possible to match currents by extracting them from collectors having substantially identical areas. Unfortunately, when the split collector transistor is subjected to mechanical stresses such as those associated with the mounting and packaging of the integrated circuit, the currents associated with collectors of substantially identical area and which occupy the same percentage of the circumference around their emitter become mismatched. Therefore, a method is needed to derive matched currents from split collector transistors which remain matched even though subjected to mechanical stress.